1. Field of the Invention
The present invention relates to an apparatus for diagnosing failure in atmospheric pressure sensors used in an engine control system and, more specifically, to a method and apparatus for diagnosing failure in atmospheric pressure sensors in a system having a first atmospheric pressure sensor, and a second, redundant atmospheric pressure sensor that provides a back up for the first atmospheric pressure sensor.
2. Description of the Background Art
Hitherto, a number of sensors have been used in an engine control system, and employment of a failure diagnosis system to diagnose whether or not these sensors are operating normally is known. For example, JP-A-2003-307152 discloses a method that includes the steps of determining whether or not an output signal of a sensor that senses a pressure in an intake manifold is within a preset range, calculating the pressure in the intake manifold on the basis of engine operating conditions, and when the output signal from the sensor is within the range, determining whether or not the difference between the pressure in the intake manifold indicated by the output signal from the sensor and the calculated pressure in the intake manifold is smaller than a set value. In the disclosed method, when the output signal from the sensor is not within the preset range or when the difference is not smaller than the set value, the calculated pressure is set as the pressure in the intake manifold.
The disclosure of JP-A-10-176582 is directed to another example of use of a plurality of sensors in an engine control system and employment of a failure diagnosis system in which an electronically controlled throttle apparatus employs two sensor systems. Each sensor system includes an accelerator sensor, a throttle sensor, and so on, and are provided for the purpose of ensuring failsafe engine control or the like. Failure diagnosis is performed by comparing sensor outputs of the two systems. For example, by comparing a deviation between a main throttle sensor and a sub throttle sensor and a predetermined threshold value, whether or not the throttle sensor is failed is determined.
Of the possible failures of a sensor system, failures such as disconnection and short circuit can be determined when a sensor output value is too high or too low with respect to a predetermined value or a predetermined range, and can be addressed as determined in advance. However, there is a case in which change or deterioration of output characteristics occur even though the sensor output value is within the predetermined range, and therefore a failure cannot be determined. In engine control for airplanes, for example, further strict standards are imposed for accuracy of failure diagnosis, and hence the failure diagnostic method in the related art is not sufficient to meet the strict standards.
On the other hand, the diagnostic method disclosed in JP-A-10-176582 can detect that either one of the two systems of sensors has a failure, but it is difficult to determine which one of the two systems of sensors has the failure when using this method.
It is an object of the invention to provide failure diagnosis method and apparatus for atmospheric pressure sensors which can reliably detect which atmospheric pressure sensor has a failure in a system having two (that is, redundant) systems of atmospheric pressure sensors.